1. Field of the Invention
This invention relates to a chipcard with an oscillator (8) integrated hereon. In particular, the invention also relates to telecommunications systems and telecommunications methods, which use such a chipcard.
2. Description of Related Art
Many portable, electronic devices require a miniaturized oscillator, which can generate a signal with a stable frequency. Crystal oscillators are frequently used for this purpose since they need little current and can easily be integrated into small devices, for example wristwatches.
A great many attempts have already been made to integrate a crystal oscillator together with various other electronic components, for example a frequency divider, into a single chip. The patent documents DE 4011795, U.S. Pat. No. 5,406,230 and U.S. Pat. No. 5,229,640, for example, describe various solutions to achieve this object. In practice, many difficulties still have to be overcome before a really reliable, inexpensive and miniaturized crystal oscillator comes on the market.
It is therefore an object of the invention to propose an improved oscillator, which can be integrated into a chip of minimal dimensions, and which can be inserted, for example, into a chipcard, including a chipcard of the xe2x80x9cplug-inxe2x80x9d format, as are used, for example, in mobile radio telephones (SIM cards).
Another object is to propose a new integrated oscillator which can generate a reference signal with a frequency that cannot be falsified, and which can be used, for example, for secure applications where a non-falsifiable determination of the time is required.
A further object is to achieve a chipcard with an integrated oscillator, with which the duration of certain processes, for example the duration of telephone calls in the case of a SIM card, can be established.
According to the invention these objects are attained with the aid of a device as described in the independent device claim and with a method as described in the independent method claim, various variants being described in the dependent claims.
In particular these objects are achieved with the aid of a new integrated oscillator with which an electrical signal is generated from an interference between two coherent light signals, the light signals being generated with one or more integrated laser transmitters.
R. P. Braun et al. describe in xe2x80x9cLow-Phase-Noise Millimeter-Wave Generation at 64 GHz and Data Transmission Using Optical Sideband Injection Locking,xe2x80x9d IEEE Photonics Technology Letters, Vol. 10, No. 5, May 1998, the possibility of generating signals with a frequency of only some megahertz from an interference between two laser signals. The described device is intended for base stations in a mobile radio network; however, it is not indicated in this document that integrated laser sources can also be used.
Other experiments in generating microwave signals from an interference between laser signals have also been described by R. P. Braun et al. in xe2x80x9cOptical Harmonic Upconversion for Microwave Generation in Bidirectional Broadband Mobile Communication System, xe2x80x9d Electronics Letters, Vol. 33, No. 22, Oct. 23rd 1997, and by R. P. Braun et al. in xe2x80x9cOptical Microwave Generation and Transmission Experiments in the 12- and 60-GHz Region for Wireless Communications,xe2x80x9d IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 4, Apr. 1998. Although all these documents concern the generation of signals in the microwave range (for example signals with a frequency of 12 or 60 GHz), signals with a lower frequency can also be generated with the same principle, for example signals which can be processed by conventional, digital logic circuits.